But we're still talking about crystals, right? The whole reason for trying to crystallise our proteins/DNA/RNA is because we ideally want a perfect arrangement of molecules. So taking as a starting hypotheses the conservative approach that if the data really looks like P21 it probably is P21 seems a good idea to me.
"if the data really looks like P21--" what are the criteria for that? For example, I believe p1 can have good-as-perfect 90deg angles, no? And also equal cell dimensions? So I don't think you will be able to tell from the positions of the spots on the detector, necessarily. Also, would it not be more rigorous to say "I can gain a lot by assuming these molecules are in p21?" Look, nobody thinks that every molecule in the crystal is identical, so that is truly a convenient assumption. The symmetry, I think, is a similar assumption at a different level.
By the way, I have always wondered whether anybody has looked into the degree of intermolecular differences possible given all of the parameters in our crystallographic models. In other words, would a microscopic observer look at the molecules in the crystal and see what looks like a crowd from a NYC street, or something more like an army formation? How much variety is there at the molecular lever, I wonder?
True: but how do you judge that those differences are within or outside of experimental noise?
Agreed!
What if by refining in P1 the parametrisation makes those side-chains different in the first place? A poorly defined Lys side-chain suddenly becomes two significantly different poorly defined side-chain?
I don't know--depends on last question I think. Jacob ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program Dallos Laboratory F. Searle 1-240 2240 Campus Drive Evanston IL 60208 lab: 847.491.2438 cel: 773.608.9185 email: [email protected] *******************************************
